Download Inheritance [Repaired]

Look at the characters below:
1) Who are their parents? What could they be called?
2) Why do they look like their parents?
Inheritance 27/9
Chromosomes, genes and DNA
Objectives:
*Define inheritance
** State the meaning of the terms
chromosome , gene and DNA
Starter:
What is inheritance?
Inheritance is transfer of characteristics or traits e.g. physical
appearance, personality, capabilities at things like sports, music etc
from one generation to the next.
• Chromosome Each chromosome is a length made of deoxyribonucleic acid
Each
genearound
(a section
of DNA)is
unit of
inheritance
in coiled.
that it
wound
molecules
of an
protein
and
very tightly
• Gene –
codes for a specific protein. Humans have about 20-25000
Adifferent
long chain
molecule made of double helix of 4 bases
genes
• DNA –
• Haploid cell is one with a single set of chromosomes (for example a gamete)
• Diploid cell is -one with a double set of chromosomes (for example any somatic
cell )
During cell division the chromosomes appear very tightly coiled at other
times they are uncoiled so that cells can use the information coded in the
DNA
animation
Mitosis and Meiosis 30/9
Objectives:
*Define mitosis and state its importance in
growth, development and asexual reproduction
** Define meiosis and state its importance in
the formation of gametes and in producing
genetic variation
H/w due in 3/10
Complete worksheets
animation
MITOSIS
MEIOSIS
Mitos
don’t
Mitosis
do
sex
Meiosis
2 daughter cells
Genetically identical to parents
diploid
In somatic cells for growth, repair,
replacement
For asexual reproduction
4 daughter cells
Genetically not Identical to parents
haploid
In sex cell producing organs e.g.
For sexual reproduction
Importance of mitosis in
Growth - where in animals?
where in plants?
All over the body
In root, shoot tips
wounds
Repair – what?
Replacement – cells which wear away or die e.g.? RBC
Asexual reproduction – e.g. Fungus, amoeba, bacteria, some plants
Genes and Chromosomes 3/10
Objectives:
*Describe the inheritance of sex based upon X
and Y chromosomes in humans
**Use the terminology of inheritance
***Distinguish between genes and alleles
H/w due in on 4/10
Write the definitions of the following words:
Genotype, phenotype, homozygous, heterozygous, dominant, recessive
Boy or girl - what decides?
The 23rd pair of chromosomes in females is
a matching pair called the X chromosomes.
Males have only one X chromosome: its
‘partner’ is a much smaller Y chromosome.
Boy or girl - what decides?
The photograph below shows all the
chromosomes in a woman’s cells. There are
23 pairs.
The photograph below shows all the
chromosomes in a man’s cells.
How do the male and female sets of chromosomes differ?
Boy or girl - what decides?
When a cell in a woman’s ovaries divides to
make egg cells, each egg receives one X
chromosome.
When a cell in a man’s testes divides to
make sperms, each sperm receives either an
X or a Y chromosome.
XX
X
XY
X
X
Y
Genetic Crosses Punnet Square
Who determines the gender of the baby, Mum or Dad?
Parental phenotype
Parental genotype
Gametes
Gametes
X
X
Female
XX
X
X
Y
XX XY
XX XY
X
x
Male
x
XY
x
X
Y
Outcome: 50% Girls + 50% Boys
Genotype
Phenotype
XX
Girl
Genotype
Phenotype
XY
Boy
Boy or girl - what decides?
Since there is an equal
chance of an X sperm or a
Y sperm fertilising the egg,
boys and girls are born in
roughly equal numbers.
50% of sperms contain an X chromosome,
the other 50% a Y.
If this sperm fertilises
the egg, the baby is a
girl.
All egg cells contain an X
chromosome.
X
X
XX
If this sperm
fertilises the
egg, the baby
is a boy.
Y
XY
Chromosomes and genes
Chromosomes resemble tiny threads
in the nucleus of a cell.
Each chromosome is a string of units
called genes: each gene is an
‘instruction’ which controls or affects
a particular feature of the body.
Chromosomes and genes
Every chromosome you received from
your mother at fertilisation has a
matching ‘partner’ from your father.
The partner chromosomes may have
identical copies of some genes, but
slightly different versions of others.
If you resemble your mum and/or your
dad, it’s because your cells contain a
mixture of their genes.
M
F
Symbols
4
The genes are represented by letters
The gene for black fur is given the letter F
The gene for brown fur is given the letter f
FF
ff
The genes must have the same letter but the
dominant gene is always in capitals
Chromosomes and genes
b
Every chromosome you received from your
mother at fertilisation has a matching ‘partner’
from your father.
B
Here,
mother’s
and
father’s
chromosomes
have
identical
versions
of these
genes...
... but
different
versions
of these.
M
F
The partner chromosomes may have identical
copies of some genes, but slightly different
versions of others.
These different or identical versions are called
alleles. When the alleles are same they are
homozygous when different heterozygous
Lets take the first pair of genes and name them as B now
since the two alleles are different lets call them B,b. In
such cases sometimes one is dominant over the other we
write the dominant one with capital letters and the other
as small letter and call it recessive. If we assume that these
genes represent eye colour and B= brown and b = blue
when B is present we can get two genotypes BB or Bb and
their phenotypes will all be brown but we can also get an
allele combination of bb which will give a blue phenotype
If BB is homozygous dominant
Bb and bb are
Chromosomes and genes
If you resemble your mum and/or your
dad, it’s because your cells contain a
mixture of their genes.
But if you have brothers or
sisters, they inherited a mixture
of your mum’s and dad’s genes
too: so why aren’t you exactly like
them?
M
F
Chromosomes and genes
Suppose that these are two of the 23 pairs of chromosomes in a
woman’s body cells.
When she makes egg cells, each egg must receive only one
chromosome from each pair. (Why is this important?)
Any egg could receive...
For just two pairs
of chromosomes,
there are four
different ways of
choosing one
from each pair.
... these
two
or these
two
or these
two
or these
two.
How many
different ways are
there of choosing
one from each of
23 pairs?
Chromosomes and genes
For just two pairs of chromosomes, there are four different
ways of choosing one from each pair.
How many different ways are there of choosing one from
each of 23 pairs?
There are 223 different ways: that’s over 8 million.
So if you have a sister, there’s a one-in-8-million chance that
the egg that grew into you contained the same set of
chromosomes as the egg that grew into your sister; and
another one-in-8-million chance that the sperm that
fertilised your egg contained the same set of chromosomes
as the sperm that fertilised your sister’s.
The chance of you and your sister getting the same set of
chromosomes from both parents is therefore one in 64
million million.
Chromosomes and genes
Remember that the chromosomes are strings of genes coded instructions that control many of your characteristics.
So if you have a sister, about half (on average) of the genes
you inherited from your parents will be the same as hers;
and half will be different. The chance of you both inheriting
exactly the same set of genes is so tiny that in practice it
never happens.
In your exercise books, write
•a paragraph headed ‘Why brothers and sisters look similar’
•a paragraph headed ‘Why brothers and sisters do not look
identical’.
Monohybrid inheritance 4/10
Objectives:
*Define monohybrid inheritance
**Explain examples of monohybrid crosses
Patterns of inheritance
Sarah can roll her
tongue into a tube,
like this:
So can her baby
brother Tim:
But her twin brother Matt
can’t do it:
Sarah’s mum can roll her tongue too, but her dad can’t. What decides who can and who
can’t?
Patterns of inheritance
Whether or not you can roll your tongue depends on which versions of a particular
gene you possess.
R
This version, R,
gives you the ability
to roll your tongue.
r
This version, r, does
not give you the
ability to roll your
tongue.
Patterns of inheritance
We all possess two copies of the tongue-rolling gene, on one of our pairs of
chromosomes.
R
R
If both your copies
are the R version,
you can roll your
tongue.
R
r
If you have one R
and one r, you can
roll your tongue.
r
r
If both your copies
are the r version,
you cannot roll your
tongue.
Patterns of inheritance
R
r
If you have one R
and one r, you can
roll your tongue.
The ‘versions’ R and r are called alleles of
this gene. If you have just one R allele and
the other is r, you can roll your tongue just
as well as if you had two R alleles. Because
of this, the R allele is described as
dominant, and r recessive.
Patterns of inheritance
Sarah
Tim
Matt
Remember, their mum can roll her tongue, but their dad can’t.
What alleles of the tongue-rolling gene must Matt possess?
What alleles of the gene must their dad possess?
How did Matt get his two r alleles?
rr
rr
One from each parent.
So, what alleles of the tongue-rolling gene must their mum possess?
Patterns of inheritance
Sarah
Tim
Matt
If their mum can roll her tongue, but passed on an r allele to Matt, she must have...
Rr
So what decided who inherited tongue-rolling and who did not?
Patterns of inheritance
When cells in Sarah’s mum’s ovaries divided
to make egg cells, each egg received either
an R or an r allele.
When cells in her dad’s testes divided to
make sperms, each sperm could only receive
an r allele.
Rr
R
rr
r
r
r
Patterns of inheritance
At fertilisation, random chance decides
whether the sperm (with one r allele) meets
an egg with an R allele, or one with an r
allele.
r
If Sarah’s mum and dad have another
child, what is the probability that he or
she will be a tongue-roller?
50%: this is the probability that the egg
will contain an R allele.
R
Rr
r
rr
Patterns of inheritance
• Mary and Jim can both roll their tongues
• Their first two children, Laura and Jason, can also
roll their tongues
• Their third child, Charlotte, cannot roll her tongue
Explain the inheritance of
tongue-rolling in Mary and Jim’s
family. What is the probability
that their next child will be able
to roll her/his tongue?
Patterns of inheritance
• Mary and Jim can both roll their tongues, so must
both have an R allele.
• But they have a child who can’t roll her tongue:
Charlotte must have inherited r from both her
parents.
• So Mary and Jim must both be Rr.
At fertilisation, random chance decides
which sperm meets which egg.
Three times out of four, fertilisation will
result in RR or Rr. Only one in four
fertilisations will give rr.
R
Half of Mary’s eggs have
R, half r.
R
r
?RR
?Rr
?Rr
?rr
Half of Jim’s sperms have
R, half r.
The probability that their
next child will be a
tongue-roller is 3/4, or
0.75, or 75%.
r
Co-dominance 7/10
Objectives:
*Explain the term codominance
**Describe the inheritance of ABO blood groups